To be cost efficient, terrestrial electrical generators under 1,000 HP use reciprocating engines as their power source. Reciprocating engines use up a lot of closed space which has to be adapted to tolerate heavy weights and medium- and low-frequency vibrations, high maintenance costs and a narrow range of fuels. Furthermore, these engines take a long time to warm up and get into condition for connecting to the power lines, which hinders its ready availability to respond to demand or else high maintenance costs when it is stopped for servicing to be performed while still hot to reduce the outage time.
Light airplanes and helicopters needing power plants under 500 HP use internal-combustion engines. Compared to turbo-engines, these engines are heavier per unit of delivered power, highly complex because of the large quantity of moving parts they contain and require periodic specialized inspections.
Light one-to-four seating helicopters are particularly penalized because there is no alternative for them other than combustion engines. Therefore, their capabilities are severely restricted by the need to carry a heavy power plant, a significant weight in terms of one or several passengers. Stresses and vibrations transmitted to the whole helicopter and to the passengers or the use of reciprocating engines further significant deter use of these helicopters.
The high market prices of both light airplanes and helicopters have made room for the use of turbines instead of combustion engines. A difference compared to the combustion engines, wherein the different strokes of the ignition cycle are carried out reciprocating in cylinders (in pulses), is that turbines carry out their ignition-compression process continuously. The turbines comprise a compression stage for producing pressurized air, a combustion chamber into which the pressurized air is admitted together with fuel and an expansion stage producing power on a rotary shaft by means of a turbine integrated to the compressor. Part of the power generated by the turbine is used for driving the compressor and the auxiliary systems, the balance is available as net power.
A feature of turbines is their ability to generate a high density of mechanical energy per volume-unit compared to combustion engines of the same power. On the other hand, in turbo-engines, dynamic high-amplitude and low-frequency stresses are transmitted to the structures since they lack massive oscillating or eccentric mechanisms.
A further competitive advantage of turbo-engines vis-avis combustion engines is the former's greater flexibility in the election of fuel. Combustion engines only use aircraft petrol which is very volatile and explosive, with the safety considerations this implies. On the other hand, turbo-engines may be fuelled with aircraft kerosene (JP1), much less volatile and explosive, natural gas, diesel-oil or practically any kind of fossil or synthetic fuel producing a lower emission of polluting gases compared to combustion engines of like power. This makes the turbo-engines more attractive for terrestrial or stationary uses, given the possibility of using cheap fuel for the generation of electricity or delivering work to a shaft. In addition, the balance of heat which is emitted as well as the high-temperature exhaust gases may be advantageously used, either for supplying a heating system or for recovery in a secondary cycle, leading to improved efficiency of the turbo-engine cycle. Furthermore, turbo-engines are less sensitive than combustion engines to loss of atmospheric pressure and low temperatures, as occurring at high flight altitudes.
Aircraft turbines are well established for the high power segment, say above 600 HP.
An important technical obstacle that must be overcome when designing a low-power turbo-engine turning at high speeds (over 25,000 RPM) is that its applications generally require a substantially lower number of revolutions per minute (RPM), meaning that an associated gear-box is necessary but which otherwise would be undesirable in that it adds weight, mechanical complexity and auxiliary systems.